Beginner code, something is not right. If and else if statement (C#)

Question

I am learning how to program so please be nice. :)

I have this error running the code:

An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll Additional information: Input string was not in a correct format.

When I type "screw you, don't tell me what to do!". When I delete the whole insult part of the code, it's working flawlessly. What am I doing wrong?

namespace ConsoleApplication6 
{
    class Program
    {
        static void Main(string[] args)
        {
            int numero1 = 5; //Declaring first variable
            int numero2 = 5; //Declaring second variable

            Console.WriteLine ("What is the answer of " + numero1 + " x " + numero2); //Asking question to the user

            int answer = Convert.ToInt32(Console.ReadLine()); //Converting the "answer" to integral variable
            string insult = Console.ReadLine(); //The user enter his insult          

            if (answer == 25) //If the answer is 25
            {
                Console.WriteLine("Good answer!"); //This message appears            
            }
            else if (insult == "screw you, don't tell me what to do!") //If the user insult me
            {
                Console.WriteLine("Wow buddy, gotta check that language!"); //The user receives this message              
            }
            else
            {
                Console.WriteLine("Dude...what?"); //If the user write anything else, he gets this message
            }
            Console.ReadKey();
        }
    } 
}

Answer 1

Do like this:

        int numero1 = 5; //Declaring first variable
        int numero2 = 5; //Declaring second variable

        Console.WriteLine ("What is the answer of " + numero1 + " x " + numero2); //Asking question to the user

        string answer = Console.ReadLine(); //Converting the "answer" to integral variable


        if (answer == "25") //If the answer is 25
        {
            Console.WriteLine("Good answer!"); //This message appears            
        }
        else if (answer == "screw you, don't tell me what to do!") //If the user insult me
        {
            Console.WriteLine("Wow buddy, gotta check that language!"); //The user receives this message              
        }
        else
        {
            Console.WriteLine("Dude...what?"); //If the user write anything else, he gets this message
        }
        Console.WriteLine("Press any key to close the application");
        Console.ReadKey();

This is a simple change that makes your code easier to understand, hopefully. You are already "hardcoding" the results so by putting 25, in a string, does not make your code less good.

Answer 2

use int.TryParseas below, if user enter non integer value your program will fail

Console.WriteLine ("What is the answer of " + numero1 + " x " + numero2);
string keyboardInput = Console.ReadLine();
int answer;
while (!int.TryParse(keyboardInput, out answer)) {
    Console.WriteLine("Invalid input, try again.");
    keyboardInput = Console.ReadLine();
}
// now read the insult
string insult = Console.ReadLine(); 

since you need two inputs you need to click enter after entering answer, then again you can type the insult and hit enter